Which electrolyte disturbance is most commonly associated with loop diuretic use in critically ill patients?

• A. Hyperkalemia
• B. Hypocalcemia
• C. Hypokalemia
• D. Hyponatremia

Answer: (C)

Loop diuretics cause potassium wasting in the kidney. By blocking the Na-K-2Cl transporter in the thick ascending limb, they reduce reabsorption of sodium, chloride, and potassium. That extra sodium reaches the collecting duct, where sodium reabsorption is coupled to potassium and hydrogen ion secretion, increasing potassium loss in the urine. This makes hypokalemia the most common electrolyte disturbance associated with loop diuretic use, especially in critically ill patients who may have limited intake and additional losses.

It's also helpful to remember that loops increase calcium excretion, so hypocalcemia can occur, but this is less common than hypokalemia. Hyponatremia can happen with diuresis as well, but the hallmark issue tied to loop diuretics is potassium wasting.